The present invention generally relates to a medical pad and related system for cooling and/or heating a patient via contact thermal exchange. The present invention is particularly apt for treating stroke and head trauma patients.
Medical pad systems for systemic cooling and/or heating of patients are known. Typically such systems include a pad that is placed on the patient. For example, the pad might be placed on the patient""s torso. A fluid, such as water or air, is then circulated through the pad. Thermal energy is exchanged between the patient and the circulated fluid to cool or heat the patient. For example, water or air at an appropriate temperature below the desired temperature of the patient may be circulated through the pad to absorb heat from the patient and thereby achieve systemic cooling.
The therapeutic use of systemic cooling for a variety of conditions has been investigated. Of particular interest, it has recently been discovered that rapid systemic cooling of stroke and head trauma patients may have significant therapeutic benefits. Stroke is a major cause of death and neurological disability. Recent research suggests that even though a stroke victim""s brain cells may lose their ability to function, the cells do not necessarily die quickly. In fact, brain damage from a stroke may take hours to reach maximum effect. Neurologic damage may be limited and the stroke victim""s outcome improved if a neuroprotectant therapy is applied within this time frame. As a result of vehicle crashes, falls and the like, many people suffer traumatic brain injury (e.g. impairment of cognitive abilities or physical functioning). Elements in the genesis of traumatic brain injury are now understood to overlap with elements in the genesis of neurologic damage in stroke victims. Delayed secondary injury at the cellular level after the initial head trauma event is now recognized as a major contributing factor to the ultimate tissue loss that occurs after brain injury.
One neuroprotectant therapy that may be applied early in the treatment process to stabilize and reduce ongoing cellular damage is hypothermia. Studies have shown that treatment with mild hypothermia, defined as lowering core body temperature 2-3xc2x0 C., confers neuroprotection in stroke victims, and may hasten neurologic recovery and improve outcomes when applied for twenty-four to seventy-two hours in cases of traumatic brain injury.
In view of the foregoing, one object of the present invention is to provide an improved medical pad and related system that can be employed to lower a patient""s body temperature rapidly and accurately.
Another object of the present invention is to provide an improved medical pad and related system that can be employed to maintain a patient in a state of mild hypothermia for an extended period.
A further object of the present invention is to provide an improved medical pad and related system that can be employed to raise a patient""s body temperature in a controlled manner.
Yet another object of the present invention is to provide an improved medical pad that yields enhanced interface with a patient""s skin.
These and other objectives and advantages are achieved by various aspects of the present invention. According to one aspect of the present invention, a medical pad for contacting and exchanging thermal energy with a patient includes a thermal exchange layer capable of absorbing and/or releasing heat from/to a patient, and an adhesive surface disposed on a skin-contacting side of the thermal exchange layer for adhering the pad to the skin of the patient. The thermal exchange layer may comprise a fluid containing layer for containing a thermal exchange fluid capable of absorbing thermal energy from and/or releasing thermal energy to the patient. The thermal exchange fluid, which may be a liquid (e.g. water) or a gas, may be circulated within the fluid containing layer from a fluid inlet to a fluid outlet.
The fluid may be circulated by drawing fluid into the fluid containing layer through the inlet and out of the fluid containing layer through the outlet under negative pressure by a pump connected downstream from the outlet. The fluid containing layer may be defined by a pair of correspondingly sized sections of a nonporous material that are welded to one another along perimeter edges thereof to form a waterproof seal. When the pad is adhered by the adhesive surface to the skin of the patient, thermal energy is exchangeable between the patient and the fluid circulated within the fluid containing layer. In this regard, the pad may be utilized in cooling and/or heating procedures depending upon the relative temperature of a patient and the fluid circulated within the fluid containing layer. As one alternative to fluid circulation, the thermal exchange layer may include electrically resistive elements therein for generating thermal energy that is transferable from the pad to the patient.
According to a further aspect of the present invention, flow path defining means may be disposed within a fluid containing layer of an improved medical pad. The flow path defining means define one or more tortuous fluid flow paths from the inlet to the outlet in each of at least two flow path layers within the fluid containing layer. The tortuous fluid flow paths inhibit the formation of boundary layers along the inside surfaces of the fluid containing layer. The flow path defining means may comprise a first plurality of elongated members that are arranged in a first layer and oriented in a first direction and a second plurality of elongated members that are arranged in a second layer and oriented in a second direction that is transverse to the first direction (e.g. to define a cross-hatch pattern). The first plurality of elongated members may be arranged within the first layer in a parallel fashion and the second plurality of elongated members may be arranged in the second layer in a parallel fashion. The two layers of elongated members may be defined by a netting material. A fluid inlet and outlet may be provided in the pad and each port may include a fluid flow port that is oriented for fluid flow therethrough in a direction that is transverse to the first and second directions of orientation of the elongated members.
According to an additional aspect of the present invention, a conformable, thermally conductive layer is disposed between an adhesive surface and fluid containing layer of a medical pad. The conformable, thermally conductive layer is sufficiently thick and is comprised of a sufficiently conformable material so as to conform to the contours of a patient""s skin and envelop skin hair. As a result, insulating air pockets between the pad and the skin of a patient are reduced. In this regard, the conformable, thermally conductive layer is preferably at least about 0.013 cm thick and is preferably comprised of a material having an elastic modulus of between about 40 and 1000 pascals. The conformable, thermally conductive layer also provides for sufficient thermal exchange therethrough between the skin of the patient and the thermal exchange layer. In this regard, the conformable, thermally conductive layer is preferably less than about 0.15 cm thick and is preferably comprised of a material having a coefficient of thermal conductivity of at least about 2.00 cal/hr-cm-xc2x0 C. so that the conformable, thermally conductive layer preferably has a minimum thermal transfer rate of at least about 13.33 cal/hr-cm2-xc2x0 C. The conformable, thermally conductive layer may comprise a first material, such as a liquid (e.g. water), suspended in a matrix defined by a second material, such as a polymer. In this regard, the liquid preferably comprises between about 30 to 95 percent by weight of the total weight of the first and second materials. The adhesive surface and thermal transfer layers in the noted arrangements may be separately comprised of distinct materials. Alternatively, a thermally conductive layer may be comprised of a hydrogel material having sufficient adhesive properties so as to integrally provide the adhesive surface. In any case, the adhesive surface should have sufficient adhesive strength to hold the pad in place yet not cause tissue damage when removed. In this regard, the adhesive surface could preferably have a peel value against skin at initial application of at least about 10 gm/inch.
According to yet another aspect of the present invention, an insulating layer may be disposed on the non-skin contacting side of a fluid containing layer of a medical pad. The insulating layer inhibits heat transfer between the surrounding air and the fluid circulated through the fluid containing layer thereby enhancing the efficiency of the pad. Preferably, the insulating layer is comprised of a material having a coefficient of thermal conductivity of less than 1.00 cal/hr-cm-xc2x0 C. and is preferably at least about 0.06 cm thick so that the insulating layer preferably has a maximum thermal transfer rate of about 16.67 cal/hr-cm2-xc2x0 C.
In a related aspect of the invention, a dual function layer may be utilized to provide one side of a fluid containing layer of a medical pad, as well as flow path defining means within the fluid containing layer. More particularly, a flexible, insulating material (e.g., a non-permeable polymer or polymer, closed-cell foam) may be fabricated into a base member having a plurality of integrally defined dimples projecting from a base portion, wherein the base member and a flexible, non-permeable film or sheet (as described above) may be interconnected to define a fluid containing layer therebetween, with the dimples both supporting the flexible sheet and defining internal fluid flow pathways. In turn, a conformable, thermally conductive layer (e.g., as described above) may be laminated to the flexible sheet. An adhesive surface (e.g., as described above) may be disposed on the outward, or skin-facing, side of the thermally conductive layer. Preferably, the base member may function as an insulating layer (e.g., as described above) and may have a density of between about 2 to 12 lb/ft3. By way of primary example, the base member may comprise at least one material selected from a group consisting of: polyethylene, polyurethane, polyvinyl chloride, and ethylene-vinyl acetate copolymers. The dimples may be provided in a variety of configurations and patterns, including cylindrical or truncated cones arranged in rows/columns so that adjacent rows and adjacent columns are offset from each other by 60xc2x0. In another arrangement, elongated, truncated, pyramidal dimples may be disposed in a herringbone pattern. Preferably, the dimples will have a height of between about 0.02 and 0.2 inches, and most preferably, between about 0.04 and 0.1 inches. One or more ribbing members may be positioned between adjacent ones of the dimples (e.g., via integral molding as part of the base member) to extend across the fluid containing layer in the direction of desired fluid flow from a fluid inlet edge to a fluid outlet edge.
It should be appreciated that several features of a pad embodiment constructed in accordance with the present invention facilitate efficient thermal transfer between the pad and the patient. For example, overall construction of the pad may be relatively thin since it is preferably operated under negative pressure. The use of a cross hatched layer of netting material within or a dual function layer with dimples to partially define the fluid containing layer facilitates a high rate of thermal transfer under negative pressure within the fluid containing layer, and further allows fluid which has absorbed/released thermal energy from/to the patient to be rapidly cycled. Because the pad may be relatively thin, it is conformable. The conformable nature of the pad, and in particular, the conformable, thermally conductive layer, permits enhanced direct contact between the pad and the patient thereby enhancing the effective area of thermal exchange between the pad and the patient. An adhesive surface particularly assures direct contact between the patient""s skin and the pad.
According to yet another aspect of the present invention, a method of exchanging thermal energy between a patient and a medical pad includes contacting the external surface of the pad with the skin of the patient in order to establish a thermal interface between the skin of the patient and the pad. A thermal exchange fluid reservoir is interconnected with a fluid inlet to the fluid containing layer. The reservoir contains a thermal exchange fluid that is capable of absorbing and/or releasing thermal energy. A pump is coupled with an outlet from the fluid containing layer. The pump is operated to establish negative pressure at the outlet and thereby draw fluid from the reservoir though the inlet into the fluid containing layer and out through the outlet.
According to related aspects of the inventive method, in the step of contacting, the pad may be adhered to the patient by bringing an adhesive surface disposed on the skin contacting side of the fluid containing layer into contact with the patient. In the step of operating the pump, the body temperature of the patient may be monitored and the pump may be operated so as to change the patient""s body temperature a predetermined amount. For example, the method of the present invention may be employed to quickly reduce the body temperature of stroke and head trauma patients about 2-3xc2x0 C. Further, in the step of operating, the fluid may be drawn through the fluid containing layer along one or more tortuous fluid flow paths defined by first and second pluralities of elongated members within the fluid containing layer or by dimples comprising a dual function backing layer. Additionally, the method of the present invention may include utilizing a conformable, thermally conductive layer between the fluid containing layer and the patient to enhance the thermal energy exchange as well as insulating the pad with a layer of insulating material disposed on the non-skin contacting side of the fluid containing layer to thereby inhibit transfer of thermal energy between the fluid circulated within the fluid containing layer and the surrounding air. As noted, the insulating layer may define the backside of the fluid containing layer as well as fluid flow pathways therewithin (e.g., via the use of dimples as noted above).
These and other aspects and related advantages of the present invention should become apparent from a review of the following detailed description when taken in conjunction with the accompanying figures.